Oxidized cellulose product and method for preparing the same



Jan. 16, 1968 w. H. ASHTON ETAL 3,364,200

OXIDIZED CELLULOSE PRODUCT AND METHOD FOR PREPARING THE SAME 2 SheetsSheet 1 Original Filed Nov. 29, 1961 w. H. ASHTON ETAL 3,364,200

Jan. 16, 1968 OXIDIZED CELLULOSE PRODUCT AND METHOD FOR PREPARING THE SAME 2 Sheets-Sheet 2 Original Filed Nov. 29, 1961 United States Patent 3,364,200 QXEDKZED CELLULOSE PRODUfJT AND METHOD FOR PREPARING THE SAME William H. Ashton, Philadelphia, and Charles E. Maser,

Levittorvn, Pa, assignors to Johnson & Johnson, a corporation of New Jersey Continuation of application Ser. No. 157,034, Nov. 29, 1961, which is a continuation-in-part of application Ser. No. 17,840, Mar. 28, 1960. This application May 19, 1965, Ser. No. 463,440

4 Claims. (Cl. 260-212) The present invention relates to surgical materials for control of bleeding and more particularly, to materials of this type composed of oxidized cellulose. This application is a continuation of our co-pending application Serial No. 157,034, filed Nov. 29, 1961 and now abandoned, which in turn is a continuation-in-part of our application Ser. No. 17,840, filed Mar. 28, 1960, now abandoned.

The control of bleeding is a serious problem in certain surgical procedures and in various types of emergency wounds. Bleeding from the kidney, brain, or liver or the persistent oozing from severed capillaries and veins, for example, is particularly difficult to control by conventional means such as suturing or ligature and in many cases is serious enough to endanger life. Surgical hemostats consisting of conventional gauze pads or similar articles impregnated with a hemostatic material such as ferric chloride, thrombin or the like, have been used for many years to arrest bleeding. Hemostats of this type cannot be left in situ in a closed wound, however, since foreign body tissue reaction would result. This is a serious disadvantage inasmuch as removal of the hemostate from the bleeding site frequently disrupts any blood clot which has formed and causes renewed bleeding. It was obvious, therefore, that a vital need existed for a hemostatic material which could be left in place in a closed wound without causing serious local tissue reaction. It was hoped that this need had been satisfied when it was discovered that oxidized cellulose not only had hemostatic properties but was absorbable in animal tissue. This led to the production and use of hemostats composed of oxidized cotton. It was found, however, that the oxidation of cotton substantially increased the inherent tendency of this material to deteriorate with age. Available oxidized cotton hemostats, which normally vary from off-white to pale yellow in color when fresh, turn yellow or brown, lose their tensile strength and eventually disintegrate, when stored at room temperature for more than 3-6 months. Exposure of oxidized cotton to strong light and elevated temperatures, such as those encountered in the tropics or in the summer months in temperate zones, greatly accelerates deterioration. It is necessary, therefore, to use previously available oxidized cotton hemostats within a short time after they are manufactured and to store them under refrigeration until used.

It is, therefore, a primary object of the present invention to provide oxidized cellulose absorbable hemostats having improved stability against deterioration on storage.

The present invention, by means of which the above and other objects are achieved, is based upon the surprising discovery that the stability of oxidized cellulose is adversely affected by water which has been used previously to remove the acidic by-products of the oxidation reaction. In the present invention these acidic by-prodnets are removed by washing with an aqueous alcohol solution containing not more than about 80 percent and preferably not more than 50 percent of Water by weight or, altematively, by the use of high vacuum techniques which eliminate the use of water altogether. Elimination of the usual water wash according to the present inven- 3,354,200 Patented Jan. 16, 1968 tion provides oxidized cellulose having dramatically improved stability against deterioration on storage.

The invention will now be described in greater detail in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an oxidized cellulose absordable hemostat of the invention in the form of a knitted fabric;

FIG. 2 is a much enlarged fragmental view showing the structure of the knitted fabric of FIG. 1; and

FIG. 3 is an enlarged View of an oxidized cellulose absorbable hemostat of the invention in the form of a pledget composed of an integrated mass of staple fibers.

Sources of cellulose The present invention is useful for improving the stability against deterioration of oxidized cellulose derived from any source including naturally occurring cellulosic materials and regenerated cellulose. More specifically, the new method may be used to improve the stability of oxidized cellulose derived from wood pulp, cotton, cotton linters, ramie, jute, paper and similar materials and regenerated cellulose or rayon produced by either the viscose or Bernberg processes. Inasmuch as the invention has its greatest utility in the surgical field, the preferred sources of cellulose are cotton and particularly regenerated cellulose since these materials are best suited for surgical purposes. Regenerated cellulose is preferred over cotton because of its uniformity of chemical and physical properties. A knitted or woven fabric is generally the most useful physical form for use in surgery, although other forms such as integrated masses of staple fiber, threads, films and cellular sponges also have utility.

As noted above, previously available oxidized cellulose absorbable hemostats have been derived from cotton. Although hemostats of this type represent a step forward in the art or" controlling bleeding they have certain inherent disadvantages in addition to their poor stability against deterioration on storage. These disadvantages are believed to stem from the lack of uniformity of the chemical and physical properties of cotton. Inasmuch as cotton is a natural product its composition is affected by growing conditions and thus batches of cotton grown in different years or different geographical areas vary in chemical and physical properties. Furthermore, cotton fibers do not have a uniform diameter throughout their length. This lack of physical uniformity makes it impossible to oxidize cotton uniformly. When oxidation conditions are chosen which would result in complete oxidation of the thicker portions of the cotton fiber, the smaller diameter portions will be over oxidized and thus will have a tendency to deteriorate rapidly. On the other hand, when oxidation conditions are chosen which would oxidize the smaller diameter portions of the cotton fiber to the desired degree, the larger diameter portions of the fiber may not be oxidized sufficiently. This is disadvantageous since the partially oxidized cotton may not be readily absorbable in animal tissue. It is apparent that the inherent lack of uniformity of cotton ultimately leads to lack of uniformity of absorption of oxidized cotton in animal tissue. Therefore, although the present invention is useful in improving the shelf life of oxidized cotton hemostats, it is preferred to employ a more uniform starting material such as regenerated cellulose in the preparation of absorbable hemostats.

Any type of regenerated cellulose may be used whether prepared by the viscose or Bemberg process, the only essential requirement being that the regenerated cellulose be a so-called bright rayon, i.e., a material which has not been dulled by the addition of titanium dioxide or similar heavy metal materials. It is obvious that heavy metals of this type and other toxic substances must be avoided if the oxidized cellulose is to be used for surgical purposes. In general the heavy metals content (lead, copper, iron) of the oxidized regenerated cellulose product should not exceed about 30 parts per million and preferably should be less than about 15 ppm.

Although not essential, it is also important that the regenerated cellulose have a uniform filament diameter in order to avoid the lack of uniformity of oxidation which is characteristic of oxidized cotton. The size of the filaments is determined by practical considerations. Filaments less than about 1 denier while theoretically useful have, so little tensile strength that it is not presently feasible to process them into a hemostat in the form of a knitted fabric, for example. On the other hand, filaments greater than about 9 denier, even though completely oxidized, may require a prolonged period of time for absorption in animal tissue. Therefore, as a practical matter regenerated cellulose composed of filaments of uniform diameter and having a denier of about 1-9 and preferably 1-3 are employed in the preparation of the preferred materials of the present invention.

As is well-known, regenerated cellulose is composed of a polymer made up of anhydroglucose units. The average number of such units per molecule of regenerated cellulose is referred to as the degree of polymerization (D.P.) of the material. The degree of polymerization of regenerated cellulose may vary from a small number of units perhaps as low as 15 up to many thousand units. Extremely low molecular weight celluloses are, of course, close to the sugars and degraded starches and thus do not have sufiicient tensile strength to be useful in the manufacture of surgical hemostats. The very high molecular weight celluloses, on the other hand, have a tendency to be less absorbable when oxidized than materials with a lower degree of polymerization. Therefore, although the degree of polymerization of cellulose for use in the present invention may vary widely, it is preferred that it be in the range from about 200-500 and is preferably about 300 when the product is to be used as an absorbable hemostat. The degree of polymerization (D.P.) of a cellulosic material may be determined by the method described by R. L. Mitchell, Industrial and Engineering Chemistry, vol. 45, p. 2520 (1953).

Although the present invention is applicable to cellulosic materials in any physical form it is most useful when applied to materials in forms which are suitable for use as surgical hemostats or for other surgical purposes. While it is possible to manufacture surgical articles from previously oxidized cellulose it is generally more convenient to manufacture the surgical articles from unoxidized cellulose and subsequently oxidize the cellulose in the article. Suitable materials include gauze, integrated masses of staple fibers, and woven, braided or twisted threads of cotton or rayon. Rayon monofilaments may also be used although they are not preferred due to the difiiculty of achieving complete oxidation of the cellulose in the interior of a high denier monofilarnent. Although woven gauze is useful, it has been found that a knitted material is preferable since it has better handling qualities than a woven fabric for surgical purposes and conforms more readily to irregularly shaped viscera. The familiar absorbent cotton of commerce may also be oxidized for use as a surgical hemostat. Here again, however, it is preferred to employ a similar material composed of staple fibers of regenerated cellulose which are formed into an integrated mass by carding, needling or other conventional means.

Preparation of oxidized cellulose Oxidized cellulose, in which the alcoholic group on the number 6 carbon atom of the anhydroglucose units has been converted to a carboxyl group, has been known for many years. It has been prepared from a variety of cellulosic materials using various oxidizing agents in both the gaseous and liquid phase. The primary consideration in the preparation of oxidized cellulose for surgical purposes is uniform oxidation of the cellulose to a predetermined degree of oxidation, i.e., percent of carboxyl content by weight. This can be achieved only by careful control of the conditions of oxidation. As noted above it is also desirable to choose a cellulosic starting material having uniform chemical and physical properties. Experience has shown that nitrogen dioxide or its dimer, nitrogen tetroxide, are the most suitable oxidizing agents for cellulose. Further, although nitrogen dioxide has been used previously in the gaseous phase to produce oxidized cotton for use in absorbable hemostats, it is preferred to conduct the oxidation reaction in the liquid phase since this provides more precise control of the reaction and better contact between the cellulose and oxidizing agent 7 thus promoting uniformity of oxidation.

The concentration of the oxidizing agent, for example nitrogen dioxide, in the reaction medium may vary from about 5-100 percent by weight. Although concentrations less than 5 percent would produce oxidation, under normal conditions an inordinately long time would be required to achieve a useful degree of oxidation. On the other hand, while percent nitrogen dioxide may be used in a gaseous phase oxidation it is not recommended in the liquid phase. This is due to the fact that pure nitrogen dioxide boils at only 20 C., thus limiting the reaction temperature which may be employed and affecting the time required to achieve the desired degree of oxidation. It is preferred to dilute the nitrogen dioxide with an inert material to reduce its concentration in the reaction mixture to about 15-75 percent. Suitable diluents include inert gases such as carbon dioxide for use in a gaseous phase oxidation, or inert, nonaqueous solvents such as carbon tetrachloride, Freon 113 (CCl F-CClF and Freon 11 (CCl F) and the like for use in the liquid phase. Freon 113 and Freon 11 are available from E. I. du Pont de Nemours and Co. The preferred diluentoxidizing agent mixture is a liquid solution containing about 20 percent by weight of nitrogen dioxide in Freon 113.

A wide range of reaction temperatures may be employed, although it is preferred not to employ substantially elevated temperatures since oxidized cellulose is adversely affected by heat. As would be expected the reaction time required to achieve a given degree of oxidation varies inversely with the temperature i.e., the higher the temperature the shorter the reaction time. It is preferred to conduct the oxidation at room temperature since this is convenient and a useful degree of oxidation can be achieved in a reasonable period of time. For example, regenerated cellulose having a denier in the range of about l-9 can be substantially completely oxidized by the liquid phase method in about 16 hours at a temperature of about 24 C. with a solution containing about 20 percent by weight of nitrogen dioxide in Freon 113. Much shorter reaction times, lower temperatures or lower concentrations of oxidizing agent may be employed when it is not necessary to achieve a high carboxyl content in the product as, for example, where a hemostat having a carboxyl content of only about 13 percent by weight or a suture having a carboxyl content of only about 8 percent by weight is required. Suitable conditions for any purpose can be found by routine trial and error. The concentration of oxidizing agent, reaction temperature, time, physical dimensions of the cellulose and other interdependent factors all affect the rate and degree of oxidation. It is preferred to use a glass-lined reaction vessel since this eliminates the possibility of contaminating the oxidized cellulose with heavy metals or other toxic materials undesirable in a surgical product.

Theoretically, oxidation of the hydroxyl group on the number 6 carbon atom of each anhydroglucose unit in the cellulose molecule would produce oxidized cellulose having a carboxyl content of 25.6 percent by weight. Such complete oxidation of cellulose is seldom desirable for surgical purposes, however, since adequate hemostatic activity and tissue absorbability are obtained at lower levels of oxidation and it has been observed that stability on storage tends to decrease as the level of oxidation is increased. Experience has shown that satisfactory oxidized cellulose absorbable hernostats should be uniformly and substantially completely absorbable in animal tissue within a period of about 15 days as judged by visual inspection although traces of the material may be identified by microscopic examination for longer periods of time. Oxidized cellulose of the present invention having an individual filament or fiber denier in the range of about 1-9 and a carboxyl content of about 12-25 percent by weight, is satisfactorily absorbable according to the above standard. It should be noted that low denier and high carboxyl content favor absorbability. Therefore, the low denier materials may be satisfactorily absorbable when oxidized to a carboxyl content of only 12-13 percent by weight whereas the higher denier materials may tend to be more slowly absorbable at this level of oxidation. It is preferred, therefore, to oxidize cellulose for use as absorbable hemostats to a carboxyl content of about 1822 percent since material having a denier in the preferred range of 19 is always satisfactorily absorbable at these levels of oxidation.

Although oxidized cellulose fabrics are the preferred embodiments, the present invention also provides new and useful absorbable sutures having improved stability on storage. However, inasmuch as sutures need not be hemostatic it is not necesary to oxidize them to the degree required in an article in which hemostatic activity is of paramount importance. In general, the blood clotting power of oxidized cellulose increases markedly with increased oxidation as does the absorbability of the material in animal tissue, although to a lesser degree. Lowering the degree of polymerization of the cellulose also increases the rate of absorbability of oxidized cellulose in animal tissue. Therefore, absorbsble sutures need only be oxidized up to the point at which a further increase in carboxyl content would no longer produce a useful increase in absorba'oility. Further oxidation would be of no utility since it would only increase the hemostatic activity of the suture which is of no importance. Therefore, satisfactory absorbable sutures can be produced having a carboxyl content of only about 3-l3 percent by weight Whereas maximum hemostatic activity is not obtained until oxidized cellulose has a carboxyl content above about 12 percent by weight. Further, inasmuch as absorbable sutures usually differ from surgical hemostats in their hemostatic and other properties it is obvious that somewhat dilferent reaction conditions are indicated for the oxidation reaction. The ratio of reactants, for example, should be chosen to produce the physical and physiological properties optimum for sutures rather than to produce optimum blood clotting power as would be required in a hemostat. It might be desirable, for example, to employ a lower concentration of oxidizing agent and a longer reaction time at a lower temperature in order to maximize tissue absorbability as opposed to the hemostatic activity of the oxidized cellulose sutures. In any case the maximum stability of oxidized cellulose sutures or other articles results only when the acidic by-products of the oxidation are removed according to the present invention irrespective of whether the suture is composed of oxidized cellulose derived from continuous filaments or spun staple fibers of regenerated cellulose, staple cotton fibers, ramie, jute, linen or any other cellulosic derivative in fiber or yarn form.

Removal of impurities When oxidized cellulose is to be used for surgical purposes, it is essential that all traces of toxic or non-absorbable substances be removed. The method of achieving this result without adversely alfecting the stability of the oxidized cellulose is the crux of the present invention. Subsequent to its oxidation, cellulose normally contains acidic and other by-products of the oxidation reaction, solvents, traces of water and residual oxidizing agent. It has been customary to remove the acidic by-products, which include nitric and other nitrogen-containing acids and low molecular weight organic acids, by the obvious expedient of washing the oxidized cellulose with water. It has now been found, however, that more than brief contact of oxidized cellulose with washes of water or an aqueous solution containing more than about percent water by volume by passing them through the perforated core and the surrounding cellulose layers gives rise to fused and charred portions and degrades the oxidized cellulose, and thus makes the material unsuitable as a hemostat. In the present invention the use of water to remove the acidic materials from the oxidized cellulose is avoided by the use of high vacuum to remove the impurities or by substituting an aqueous alcohol for water in the washing procedure. Alcoholic solutions for the latter purpose should contain at least about 20 percent alcohol and may contain as much as about 80 percent alcohol by volume. Conversely these solutions may contain as little as about 20 percent water and should not contain more than about 80 percent water by volume. Solutions containing about 50 percent of alcohol and 50 percent water by volume are preferred. The aqueous alcohol solutions should not contain sufiicient water to degrade the oxidized cellulose product in any case.

The new washing procedure employs three different solvents. The oxidized cellulose is washed initially with a nontoxic, inert, nonaqueous solvent for the oxidizing agent. This may be the same solvent employed during the oxidation reaction or a different solvent. Carbon tetrachloride, Freon 113 and Freon 11 among others are suitable solvents when the oxidizing agent to be removed is nitrogen dioxide. The oxidized cellulose is then washed with a nontoxic, aqueous alcohol solution which removes acidic by-products of the oxidation reaction such as nitric acid. The product is then given a final washing with an inert, nontoxic, nonaqueous solvent having an afllnity for water, such as a substantially anhydrous lower alcohol, in order to remove traces of water from the product.

An aqueous solution of any alcohol sufliciently miscible in water to form a solution containing at least 20 percent alcohol by volume may be employed in the second step of the washing procedure. Of the lower alcohols, which are soluble in water, ethyl alcohol and the propyl alcohols are preferred. Methyl alcohol is normally avoided because of its toxicity when the oxidized cellulose is to be used for surgical purposes. The butyl alcohols may also be employed, although these are less preferred due to their limited solubility in Water and the possibility of physiological complications. Isopropyl alcohol is the solvent of choice, as opposed to ethyl alcohol and n-propyl alcohol, due to its low cost.

The preferred solvents for removal of Water in the thi:d step of the series are lower alcohols which are sufliciently anhydrous to have an aflinity for water. Here again methyl alcohol is avoided because of its toxicity and the butyl alcohols because of their lower afi'inity for water. Ethyl alcohol and the propyl alcohols are preferred. Substantially anhydrous isopropyl alcohol is especially preferred because of its lower cost. Commercially available 99 percent isopropyl alcohol is preferred, although 95 percent or even percent alcohol can be used in the last step.

The advantages of the present invention can be obtained by any method of removing impurities, oxidizing agent, and by-products of the oxidation reaction from the oxidized cellulose as long as the cellulose is not treated with a solution containing more than about 80 percent of water by volume. Oxidized cellulose may also be subjected to a vacuum for this purpose. The latter method is not generally preferred, however, since it does not provide as complete removal of the impurities as the preferred washing procedure described above.

When the preferred washing procedure is employed, the residual anhydrous alcohol in the oxidized cellulose may be removed by drying at room temperature with a current of forced air. An oxidized cellulose product obtained in this, Way is completely free from toxic, nonabsorbable substances and thus is suitable for surgical purposes.

Sterilization When oxidized cellulose is to be used for surgical purposes, it is desirable that it be made available to the surgeon in a presterilized form since it is subject to deterioration by heat and moisture and, therefore, does not lend itself to steam sterilization by the technique usually employed in hospitals. Any method which will produce a sterile product without degrading the oxidized cellulose may be employed. Suitable sterilization methods include the electron beam technique, the use of cobalt-60 irradiation and the use of sterilizing gases. Pure ethylene oxide cannot be used since it reacts vigorously with oxidized cellulose producing heat which tends to degrade the product. Ethylene oxide can be used, however, when mixed with sufficient amounts of an inert gas such as carbon dioxide. Formaldehyde sterilization is preferred, however, because of its convenience and efliciency. It has also been discovered that sterilization with formaldehyde according to the procedure described below improves the stability of oxidized cellulose against deterioration.

The following specific examples illustrate the best mode of practicing the invention presently known. They should not, however, be construed as limiting the scope of the invention.

EXAMPLE I A uniformly and completely absorbable, hemostatic surgical gauze may be prepared as follows. Continuous, uniform diameter filaments of 1.6 denier composed of bright rayon made by the viscose process are assembled by conventional means into a 90 filament yarn having a total denier of 150. This yarn is knitted on a Wildman 28 cut, spring needle knitting machine into a fabric of plain jersey construction having a weight of about one pound per 13 square yards and a count of 18 courses and 18 wales per linear inch. The knitted fabric is attached to and wound loosely around an elongated, perforated tubular core and is then placed in a glass-lined reaction vessel provided with means for uniformly circulating liquid through the perforated core and the surrounding fabric. Twelve pounds of Freon 113 (CClQE-CCIE), the chosen reaction medium, is charged to the reaction vessel per pound of cellulose and circulated through the fabric. Three pounds of dinitrogen tetroxide (N is then charged to the reaction vessel per pound of cellulose to bring the concentration of the oxidizing agent to about 20 percent by weight of the liquid phase. The liquid phase is maintained at a temperature of about 24 C. and continuously circulated through the fabric for about 15.5 hours at the end of which time the rayon is uniformly oxidized to the desired extent i.e., about 18-22 percent carboxyl by weight. The liquid phase is then drained from the reaction vessel. The fabric is now ready for the critical washing procedure which provides the oxidized cellulose with its hitherto unobtainable stability against deterioration.

Carbon tetrachloride (Freon 113 or Freon 11 might also be used) is charged to the reaction vessel containing the oxidized cellulose, circulated through the fabric for about 15 minutes, and then drained off. This procedure is repeated twice for a total of three washes using fresh carbon tetrachloride each time. The same procedure is used to wash the material with fresh batches of an aqueous solution containing 50 percent of isopropyl alcohol by volume until the pH of the wash liquor is about 3.1. Three aqueous alcohol washes are usually sulfi- 8. cient. It is the substitution of these aqueous alcohol washes for the usual water wash which provides the increased stability against deterioration which is characteristic of the new oxidized cellulose of the present invention. The washing procedure is then repeated twice more with fresh batches of 99 percent isopropyl alcohol to remove residual water from the fabric. The fabric is then dried at room temperature by means of forced air. The oxidized fabric is then cut into pieces of appropriate size for surgical purposes, packaged and sterilized.

Sterilization of the oxidized regenerated cellulose is conveniently carried out after the hemostats composed of this material have been placed in individual packages. The unsealed packages are placed in a sterilization chamber. After the chamber is closed and sealed, the contents of the chamber are heated to about F. and the internal pressure is reduced to the equivalent of about 25 inches of mercury by evacuation of air. A solution containing 90 parts of aqueous formaldehyde (37 percent CH O) and 10 parts of glycerin by weight is vaporized by heating in a second vessel and the resulting sterilizing vapor is introduced to the sterilization chamber. Suflicient formaldehyde is employed to produce a concentration of about 10-100 mg. of formaldehyde per liter of sterilization chamber volume. Introduction of the sterilizing vapor raises the temperature of the material in the sterilization chamber to about F. This temperature is maintained for one hour at the end of which time the packages and their contents are sterile. After the sterilizing vapor is evacuated from the sterilization chamber, the packages are removed and sealed under sterile conditions.

A sample of oxidized regenerated cellulose produced as described in this example was found to have a total heavy metals content of 7.5 parts per million and the following adidtional chemical analysis:

TABLE A Oxidized rayon Percent by knitted fabric: weight CH O 0.36 COOH 19.1-20.3 N 0.24 Ash 0.145

The degree of polymerization of the regenerated cellulose from which the material of Table A above was prepared was determined several months later to be about 230.

Knitted fabric, absorbable, hemostats made by the procedure of Example I from regenerated cellulose filaments of 1 and 3 denier were found on analysis to have carboxyl contents of 19.8 and 19.4 percent by weight respectively.

EXAMPLE II Absorbable, surgical hemostats in the form of pledgets of integrated oxidized cellulose staple fibers may be prepared as follows. Chemically crimped, bright rayon staple fibers havinga staple length of 1% inches and a fiber denier of 1.6 are carded into a web by conventional means. The staple fibers may be made by the methods described in R. D. McNeer et al. US. Patent 2,821,489, issued January 28, 1958, and R. T. Carney and I. E. Corr US. patent application, Serial No. 729,084, filed April 17, 1958, now abandoned. The Web of carded staple fiber is attached to, and wound loosely around, an elongated perforated tubular core. The core and web are then placed in a glass-lined reaction vessel provided with means for circulating liquid through the perforated core and the surrounding web. The procedure of Example I is employed except that the oxidized material is washed until the aqueous isopropyl alcohol wash liquor has a pH of about 3.5 to obtain absorbable, surgical hemostats in the form of pledgets of integrated, oxidized, regenerated cellulose, staple fibers. A product obtained in this way had a heavy metals content of 2-2.5 parts per million and the following additional chemical analysis.

ABLE B Percent by weight The above procedure may also be employed to treat an interwoven mat of the staple fiber formed by conventional carding and needle looming procedures. Au oxidized cellulose mat obtained in this way was washed until the pH of the aqueous isopropyl alcohol solution was 3.7. The product had a heavy metals content of about 9 parts per million and the following additional chemical analysis.

TABLE C Oxidized rayon carded and ncedled staple Percent by fiber pledgets: weight CH O 0.776 COG'H 191-212 N .29 Ash 0.146

Solubility characteristics of oxidized cellulose It has been observed that the absorbability of oxidized cellulose in animal tissue is related to the solubility of this material in aqueous alkaline solutions and that both of these characteristics are affected by the physical dimensions such as the denier and the degree of oxidation of the oxidized cellulose. In general, low denier and high carboxyl content favor solubility in alkaline solutions and absorbability in animal tissue. Materials which will be satisfactorily absorbable in animal tissue within a short enough period of time to obviate the possibility of causing serious tissue reaction are generally those which are soluble in a 1.0 percent aqueous solution of sodium hydroxide within minutes. Samples of oxidized cellulose prepared accordin to the present invention from regenerated cellulose filaments of various deniers had a heavy metals content of about 6 parts per million and the following additional chemical analysis.

TABLE I) Oxidized regenerated Percent by cellulose: weight CH O 0.34 COOH 19.7 N 0.22 Ash 0.04

The solubility-denier characteristics of these samples are shown in Table E below.

TABLE E Time Required for Complete Solution Denier of Cellulose Prior to 1.0 Fercent 2.5 Percent 3.0 Percent Oxidation Aqueous Aqueous Aqueous NaOH Na CO NaHCO 13 see 10 min. 45 sec 18 hrs. 16 sec 11 min. 20 sec 26 hrs. 26 sec 11 min. 52 sec 72 hrs. 2 min. 10 sec 12 min. 30 sec of oxidized cellulose to select satisfactorily adsorbable materials.

Stability Cellulosic materials, as is well-known, have a tendency to degrade with age. This degradation is believed to be caused by the disintegration of the cellulose molecule into smaller molecular fragments and is evidenced by discolora tion of the cellulose and loss of tensile strength. Inasmuch as cellulosic materials are used in a variety of physical forms such as threads, integrated masses of staple fibers, and woven or knitted fabric, for example, each of which requires a different method of testing its tensile strength, it is difiicult to compare degrees of degradation of difierent forms of cellulose on the basis of loss in tensile strength alone. Experience has shown, however, that the loss in tensile strength of cellulosic materials in any physical form is directly proportional to the percentage of the material which is soluble in water. It has been found convenient, therefore, to compare the stability against deterioration of different samples of oxidized cellulose on the basis of the percentages of the materials which are soluble in Water under standardized conditions. The following standard test procedure is used for this purpose.

Samples of equal size or preferably equal weight of different oxidized cellulose materials to be compared are placed in individual one ounce glass vials filled with distilled water and allowed to stand for 17 hours in a constant temperature environment at 70 F. The contents of each of the vials is then filtered through a coarse fritted glass funnel. The filtrate and residue from each sample are then transferred to individual tared aluminum weighing dishes, weighed, and evaporated to dryness on a hot plate. The individual dishes containing the residue from each sample are then cooled and weighed again. The weight of the filtrate is obtained by substracting the weight of the dish and residue from the total weight of filtrate, dish and residue prior to the evaporation. The percentage of water soluble material in each sample is then determined by the following formula.

mg. filtrate soluble material in the sample by weight The percentage of soluble material in the samples of oxidized cellulose is then compared. A high percentage of soluble material in a sample indicates a high degree of degradation and consequently a material of poor stability.

The standard test described above was applied to samples of oxidized cellulose prepared according to the present invention and the results compared with those obtained by testing samples of oxidized cellulose prepared according to the methods of the prior art which employed a water wash subsequent to oxidation of the cellulose. Samples of oxidized cellulose were also tested in which 2 percent by weight of concentrated nitric acid had been added to the reaction mixture during the oxidation of the cellulose in order to illustrate the deleterious effect of the acidic lay-products of the oxidation reaction on the stability of oxidized cellulose and thus the necessity for complete removal of these materials.

The samples of oxidized cellulose of the present invention were prepared bythe procedure of Example I. The oxidized cellulose of the prior art was prepared as described in Example I except that the aqueous alcohol wash was omitted and a wash with Water substituted. The third sample of oxidized cellulose was prepared according to the procedure of Example I, and according to the present invention except for the addition of sufiicient concentrated nitric acid to the Freon 113-nitrogen dioxide reaction mixture to give a concentration of 2 percent by weight. Samples of the three batches of oxidized cellulose were placed in constant temperature storage at 11 70, 120, and 140 F. and the percentage of soluble material in each of the materials was determined after 2 months and 3 months aging at each of the three temperatures. The results of these tests are summarized in 70 and 120 F. The Water soluble content of the two materials was determined by the standard procedure described above prior to aging and at the end of 1 and 3 months aging respectively. The data obtained are set out Table F below. 5 in Table G below.

TABLE F Percentage of Water Soluble Percentage of Water Soluble Material After 2 Months Material After 3 Months Oxidized Cellulose Sample Aging Aging 70 F. 120 F. 140 F. 70 F. 120 F. 140 F.

Washed with 50 Percent (v./v.) Aqueous Isopropyl Alcohol 7. 06 11.2 30. 6 5.0 18. 3 33.1 Washed With Water 8. 4 l5. 95.0 18. 5 66.1 92. 5 Nitric Acid Added During Oxidation Washed With 50 Percent (v./v.) Aqueous Isopropyl Alcohol 6.7 G 1. 5 7. 5 9. 1 92.0 96. 0

TABLE G Percentage Percentage of Percentage of of Water Water Soluble \Vater Soluble Soluble Material After Material After Oxidized Cellulose Sample Material 1 Months Aging 3 Months Aging Prior to Aging 70 F 120 F. 70 F 120 F.

OxidizedRayon Unsterilized 1. 3 7. 8 9. 4 8. 9 17. 7 Oxidized Rayon Sterilized by 01120 1. 3 5. 2 7. 6 4. 5 12. 7 Oxidized Cotton Unster zed 7. 6 25.0 30. 8 18. 8 54. 5 Oxidized Cotton St A comparison of the percentages of water soluble material in the various samples tested is dramatic evidence of the substantial improvement in stability against deterioration which is characteristic of oxidized cellulose prepared according to the present invention. The new oxidized cellulose can be readily distinguished from that prepared according to the teachings of the prior art by the fact that it invariably has a water soluble content of less than about 15 and usually less than 10 percent by weight after dry storage at 70 F. for 3 months whereas the prior art materials invariably have a water soluble content of more than about 10 percent and normally more than percent by weight after storage under these conditions.

The data in Table F above, showing the percentage of water soluble material in aged oxidized cellulose prepared in the presence of added nitric acid, when compared with the data on material prepared by the invention, clearly shows the adverse effect of nitric acid, a by-prodnot of the oxidation reaction on the stability of oxidized cellulose and thus the necessity for complete removal of this material.

It may be seen, therefore, that oxidized cellulose treated to remove acidic by-products of the oxidation reaction without contacting the material with water or aqueous solutions containing more than about percent water are so much more stable than similar materials of the prior art that they are useful for surgical purposes long after the prior art materials have lost sulficient tensile strength for this purpose.

A quantity of freshly prepared commercially available unsterilized oxidized cotton surgical hemostatic material was obtained for comparison with freshly prepared oxidized regenerated cellulose produced according to Example I. It is believed that the oxidized cotton was prepared according to the methods of the prior art in which the oxidation is conducted in the gaseous phase and followed by washing the product with water. Samples of the oxidized rayon and oxidized cotton, both unsterilized and sterilized with formaldehyde according to the procedure of Example I were aged under identical conditions at The data in Table G above clearly show that oxidized regenerated cellulose of the present invention is markedly superior to commercially available oxidized cotton in stability against deterioration. The data also show the unexpected beneficial effect on the stability of oxidized cellulose which is obtained by sterilization of these materials according to the procedure of Example I. It is noted, further, that the formaldehyde sterilization has a greater beneficial effect on the stability of oxidized regenerated cellulose than it does on oxidized cotton.

Hemoslatic activity The hernostatic activity of the oxidized cellulose materials of the present invention maybe measured by the following procedure. Four dogs are anesthetized with sodiurn pentobarbitol (33 mg./kg. of body Weight) and their spleens exposed. Multiple tests are carried out on each spleen as follows: criss-cross incised wounds, about 4 mm. in depth and 8 mm. in diameter are inflicted, and the sample of the oxidized cellulose under investigation is applied over the wound. A plastic plate with a circular hole 8 mm. in diameter is placed over the test material in such a way that all blood flowing from the wound must pass through the oxidized cellulose. The time required for the test material to control bleeding i.e., arrest the flow of blood, is observed. The time required to arrest bleeding affords a basis for comparing the hemostatic activity of different materials. The normal blood clotting time in dogs is about 6 minutes when no artificial hemostasis is applied. A knitted fabric of oxidized cellulose prepared according to the procedure described in Example I was tested and observed to arrest bleeding in about 2.5 minutes.

Clinical experience Oxidized regenerated cellulose prepared as described above is inherently hemostatic. When exposed to whole human blood it is converted into a dark brown or black gelatinous mass, which appears to form, in effect, an artificially produced clot within the openings of the bleeding vessels and in the surrounding area. Hemostasis becomes 13 complete in approximately one or two minutes in humans. The material does not enter into the normal physiologic clotting mechanism per se, and for that reason is effective in controlling bleeding in many cases of hemophilia, thrombocytopenic purpura and other blood dyscrasiae.

Oxidized regenerated cellulose produced as described above has been intensively studied both experimentally and clinically to determine the rate and extent of its absorption in body tissue. Pieces of the knitted and carded fiber types, of uniform size weighing 75 mg. where implanted subcutaneously in rats by the Frantz-Lattes technique and the gross appearance of the subcutaneous implants and surrounding sites recorded. Seven days after implantation, the oxidized regenerated cellulose implants had the appearance of a soft gelatinous mass; tissue reaction being slight. At the end of fifteen days, the implanted material was observed to be completely absorbed with no evidence of inflammation. Necropsy studies in humans have been reported in whom the material was implanted in the course of various surgical procedures, and who died of causes not directly related to their surgery. In such patients, autopsies were performed at intervals of from 1 to 77 days postoperatively. In the longer term specimens the fabric could not be identified grossly, although microscopically small shreds of debris could be detected in areas of subsiding tissue reaction. As a matter of record, no toxic or other untoward reaction has been observed in the course of either extensive animal or h man use.

The absorbable hemostatic knitted fabric, carded fiber pads, sutures and other articles of the present invention have broad surgical applications. By helping to reduce the risk of uncontrollable hemorrhage, the new materials extend the range of surgical procedures which may be undertaken with relatively greater safety. Complete absorption without tissue reaction raises the ratio of normal recoveries, particularly in dificult surgical procedures. The knitted fabric is particularly useful in general surgery for the control of capillary or venous bleeding or small arterial hemorrhage where conventional means of control are technically impractical. Such bleeding may occur in gall bladder and bile duct surgery, partial hepatecomy, resections or injuries of the pancreas, spleen, kidneys, prostate, bowel, breast, or thyroid and in amputations of the extremities. In well over 160 consecutive human cases ranging in age from two months to 77 years, the material was found to be effective and well accepted physiologically in such major procedures as liver biopsy, advanced malignancies, extensive thoracic and cardiovascular surgery, and general abdominal procedures including cholecystectomy and colectomy. In several instances the new hemostatic material was considered life-saving. In no instance was wound infection, toxic reaction or death attributed to the absorbable hemostats of the invention. Apparently the presence of local infection is not in itself a contraindication to the use of these materials although, needless to say, no obstruction to drainage should exist under such conditions. One investigator found no evidence of untoward postoperative effect even in the presence of grossly contaminated wounds or leakage of infected urine.

In addition, owing to its toughness, the new knitted fabric hemostat lends itself very well indeed to tamponade of bleeding from solid viscera, when used as a bolster beneath mattress sutures. Reported cases include many types of urologic surgery in addition to prostatectomy, speno-renal shunts, pancreatomy, excision of acute aneurysm, and other major vascular procedures. Another investigator has recorded the use of these materials in a series of 100 patients in various surgical situations where rapid hemostasis was desirable. In 41 cholecystecomy cases, hemostasis was found to be excellent or good in all instances where the material was implanted in the gall bladder bed. In all instances, healing occurred without incident. The knitted fabric absorbable hemostat was also used in 34 hemorrhoidectomies with completely effective hemostasis. There is relatively little bulk to the material so that sphincteric spasm (and consequent pain) due to bulk per se (e.g., a petroleum jelly pack) was minimized. There is no need to remove the new hemostats manually as the material becomes jelly-like and is passed spontaneously in 23 days in the Sitz bath. Finally, as the material is reabsorbed by the body, there is no need to anticipate any foreign body granuloma formation as has been observed with other types of hemostatic packing. In more massive types of surgery, such as the resection of large intra-abdominal neoplasms, abdominoperineal resections and vagotomies, it was found that persistent oozing could be effectively controlled with the new hemostats in all cases without any postoperative problems resulting from leaving the material in situ.

These materials have also been found to be extremely effective in controlling bleeding from the lacerated surface of the liver esulting from stab wounds of the abdomen. In referring to eight such cases an investigator has commented that all patients recovered and none required re-operation. There were no untoward results attributed to the use of the hemostat. In thirteen instances of abdominal stabbings, the material, in addition to being used in some cases to control bleeding from a traumatized viscus, was also used locally to control bleeding in the surface wound. All wounds healed per primarn, and no side reactions were observed. The new absorbable hemostat also is useful as a primary dressing for donor sites. Several investigators have noted that when so used, primary bleeding is quickly controlled and potentially copious secondary ooze is prevented. As healing progresses, that portion of the hemostatic material which becomes wetted with blood gradually dissolves so that the dressing is easily removed without sticking or reactivation of bleeding at the time of removal (7-10 days). There is no delay in healing, so that not only is bleeding adequately controlled, but epitheliazation is completed normally. Somewhat the same considerations apply to the use of the new materials in the treatment of minor emergency wounds with loss of substance. When used as a primary dressing on such wounds, bleeding is quickly controlled, thus often avoiding the necessity of suturing or more extensive procedures. The dressing can subsequently be removed without sticking. In the light of the evidence presented, the new material has been found excellent for the prompt control of hemorrhage under emergency or less than ideal conditions such as may occur in accidental situations.

One of the most dramatic fields of usefulness for oxidized regenerated cellulose is found in cardiovascular surgery. Investigators have found the fabric type adjunctively useful in connection with the implantation of large textile grafts, including those of the abdominal aorta. Many such grafts leak or weep considerably, even when pre-clotted. Such seepage can be controlled by covering the graft with a layer or two of the oxidized regenerated cellulose gauze prior to release of the proximal and distal clamps. There is usually sufiicient blood in the field to react with the gauze and form a closely adherent sheath-like clot about the graft which effectively prevents oozing when the clamps are released. When the flow has been re-established and all bleeding controlled, the fabric can either be removed or left in situ since absorption of the gauze has been shown to occur Without constriction of the graft or other untoward incident.

Neurologic procedures offer an important field of usefulness for the carded fiber pads of oxidized regenerated cellulose in controlling punctate bleeding from the brain itself and for many other purposes. Oozing from the calvarium during prosthetic repair of a skull defect, for instance, is controlled simply by laying a pad over the under surface of the flap at the time it is turned back and then removing it on completion of the operation. Hemorrhage from the dura or brain tissue is controlled simply by applying a small pledget of the carded fiber 15 to the bleeding point. In quickly adheres and is completely absorbed with no local reaction or neurologic irritation, makin removal unnecessary.

Both the new absorbable hemostatic gauze fabric and carded fiber pads are well adapted to many otolaryngologic procedures. When used to control spontaneous nasal hemorrhage that requires packing, the material not only provides prompt hemostasis, but is easily removed after 12 to 24 hours without causing secondary hemorrhage. Other indications include: control of postoperative adenoid hemorrhage postnasal packing, packing following radical mastoidectorny, submucous resection of the nasal septum, radical ethmoidectomy, and control of the oozing which may occur during tonsillectomy. The material need not be left in place, but can usually be gently removed at the conclusion of the procedure without re-initiating bleeding. It should be emphasized, however, that this is not a substitute for ligation of bleeding points wherever possible, since disregard of this point may lead to secondary hemorrhage.

The new absorbabie hemostats find many applications in oral surgery. Bleeding problems are controlled following single or multiple tooth removal, alveolectomy, intermediate or secondary hemorrhage, inipactions, biopsies and other procedures in the oral cavity. A strip of hemostatic material may be used on the ridge area of immediate dentures to prevent seepage into the denture. Inasmuch as the new materials achieve hemostasis by virtually providing an artificially produced clot, independent of normal blood-clotting mechanisms in the wound, it is extremely useful and often life-saving in the control of post-extraction or other operative bleeding in hemophilia, thrombocytopenic purpura and other blood dyscrasiae. The knitted fabric of the invention has been used in over 200 surgical procedures about the oral cavity and the control of severe nosebleed. The investigator was as irnpressed with the ease of handling as he was with the superior hemostatic effect of the new oxidized regenerated cellulose materials. In the postoperative management of full mouth extractions, optimal results are achieved by Opening up the material slightly to cover a greater surface area with a thin layer so that the gauze can be laid over the sockets lightly. It is not necessary or desirable to use large amounts for effective hemostasis. Indeed, excessive wadding may delay healing or cause other possible complications. Results were also excellent when the hemostats were used in excision of lesions in the mouth, on the tongue, and during other radical maxillo-facial procedures. Unless the material was misused, healing was always excellent and uncomplicated. Best results were obtained when small amounts of the fabric were held gently over the bleeding surface.

In View of the foregoin disclosures, variations or modifications thereof will be apparent, and it is intended to include within the invention all such variations and modifications except those which do not come within the scope of the appended claims.

What is claimed is:

1. In the preparation of oxidized cellulose by the process of treating cellulose wound in layers around a perforated core with an oxidizing agent selected from the group consisting of nitrogen dioxide, nitrogen tetroxide and mixtures thereof, washing the resulting oxidized cellulose With a nontoxic water-immiscible solvent for said oxidizing agent, washing said oxidized cellulose first with a water soluble lower aliphatic alcohol, and subsequently washing the oxidized cellulose with a substantially anhydrous lower aliphatic alcohol having an affinity for water, wherein said oxidation by said oxidizing agent and said washings are effected by passing them through said perforated core and the surrounding cellulose layers, the improvement wherein washes consisting of an aqueous solution of a water soluble lower aliphatic alcohol containing said alcohol in a concentration range from about 20 percent to 80 percent alcohol by volume are substituted for the first of said alcohol washes.

2. In the preparation of oxidized cellulose by the process of treating cellulose wound in layers around a perforated core with nitrogen dioxide, washing the resulting oxidized cellulose with a nontoxic water-immiscible solvent for said oxidizing agent, washing said oxidized cellulose first with a water soluble lower aliphatic alcohol, and subsequently washing the oxidized cellulose with a substantially anhydrous lower aliphatic alcohol having an afiinity for water, wherein said oxidation by said nitrogen doxide and said washings are effected by passing them through said perforated core and the surrounding cellulose layers, the improvement wherein washes consisting of an aqueous solution of a water soluble lower aliphatic alcohol containing said alcohol in a concentration range rom about 20 percent to 80 percent alcohol by volume are substituted for the first of said alcohol washes.

3. In the preparation of oxidized cellulose by the process of treating cellulose wound in layers around a perforated core with nitrogen dioxide, washing the resulting oxidized cellulose with carbon tetrachloride, washing said oxidized cellulose first with a water soluble lower aliphatic alcohol, and subsequently washing the oxidized cellulose with a substantially anhydrous lower aliphatic alcohol having an affinity for water, wherein said oxidation by said nitrogen dioxide and said washings are effected by passing them through said perforated core and the surrounding cellulose layers, the improvement wherein washes consisting of an aqueous solution of isopropanol containing about percent alcohol by volume are substituted for the first of said alcohol washes.

4. In the preparation of oxidized cellulose by the process of treating cellulose wound in layers around a perforated core with nitrogen dioxide, washing the resulting oxidized cellulose with CCl FCClF washing said oxidized cellulose first with a water soluble lower aliphatic alcohol, and subsequently washing the oxidized cellulose with a substantially anhydrous lower aliphatic alcohol having an afiinity for water, wherein said oxidation by said nitrogen dioxide and said washings are effected by passing them through said perforated core and the surrounding cellulose layers, the improvement wherein washes consisting of an aqueous solution of isopropanol containing about 50 percent alcohol by volume are substit uted for the first of said alcohol washes.

References Cited UNlTED STATES PATENTS 9/1948 Kenyon et al. 260-212 XR OTHER REFERENCES DONALD E. CZAJA, Primary Examiner.

LEON 3. BERCOVITZ, Examiner.

R. N. MULCAHY, Assistant Examiner, 

1. IN THE PREPARATION OF OXIDIZED CELLULOSE BY THE PROCESS OF TREATING CELLULOSE WOUND IN LAYERS AROUND A PERFORATED CORE WITH AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF NITROGEN TETROXIDE AND MIXTURES THEREOF, WASHING THE RESULTING OXIDIZED CELLULOSE WITH A NONTOXIC WATER-IMMISCIBLE SOLVENT FOR SAID OXIDIZING AGENT, WASHING SAID OXIDIZED CELLULOSE FIRST WITH A WATER SOLUBLE LOWER ALIPHATIC ALCOHOL, AND SUBSEQUENTLY WASHING THE OXIDIZED CELLULOSE WITH A SUBSTNATIALLY ANHYDROUS LOWER ALIPHATIC ALCOHOL HAVING AN AFFINITY FOR WATER, WHEREIN SAID OXIDATION BY SAID OXIDIZING AGENT AND SAID WASHINGS ARE EFFECTED BY PASSING THEM THROUGH SAID PREFORATED CORE AND THE SURROUNDING CELLULOSE LAYERS, THE IMPROVEMENT WHEREIN WASHES CONSISTING OF AN AQUEOUS SOLUTION OF A WATER SOLUBLE LOWER ALIPHATIC ALCOHOL CONTAINING SAID ALCOHOL IN A CONCENTRATION RANGE FROM ABOUT 20 PERCENT TO 80 PERCENT ALCOHOL BY VOLUME ARE SUBSTITUTED FOR THE FIRST OF SAID ALCOHOL WASHES. 